fix: update store file to use current directory instead of parent directory

[The0mikkel]

This update fixes #20 by updating the store file location from the same directory, to the parent directory, which was introduced by mistake in 27085b4.

This does cause a breaking change to the current version, and all users are expected to update their deployment to use the current directory (the current configuration in the docker-compose.yml files provided).
If you have not update the docker-compose.yml files, you should take a copy of the /challenge_issues.json, and store it in the /app/challenge_issues.json before stopping the container. If the data stored in /challenge_issues.json is not backed up before updating, data loss may occur.

[Copilot]

Pull request overview

Updates the on-disk store location so the bot reads/writes challenge_issues.json in the container’s working directory (/app), aligning with the provided docker-compose.yml volume mount and fixing the regression described in #20.

Changes:

• Adjust Store.MAPPING_PATH to use a single os.path.dirname(__file__), so the JSON store resolves to /app/challenge_issues.json in the Docker image layout.

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[MikkelHebel]

This fixes Docker but just moves the bug to local dev. python src/main.py runs from the repo root, so removing the second dirname puts the file in src/ instead of at the root.

os.getcwd() might be more robust here than file, since that's already /app in Docker and the repo root locally.